Instantaneous hot water appliance

ABSTRACT

An instantaneous hot water appliance uses three loops. The first loop is an open loop that receives source water. Heat is extracted from the source water by a heat pump. The heat is supplied to a utility liquid, such as water, that is circulated within the closed loop. The resulting cooled source water may be used for other purposes. Heat exchange between the utility water in the closed loop and a second open loop heats domestic hot water within the second open loop. Domestic hot water is available on demand, eliminating or reducing the need for domestic hot water storage tanks and storage of large quantities of domestic hot water. In the present invention, fluctuations in condenser water temperature are dampened internally by a compressor control system as described herein that may be supplemented by a condenser water buffer.

BACKGROUND OF THE INVENTION

The use of electric powered heat pumps to heat domestic water isparticularly useful where fossil fuels are either not available or arerestricted to meet air pollution standards and/or to meet global warmingprevention objectives for heating uses. Furthermore, heating water witha heat pump has a high efficiency compared to electric resistanceheating. It is conceivable that heat pump water heating will consume 25%of the electric power of electric resistance heating for the same load.

Conventional heat pump water heaters produce domestic hot water directlyfrom the condenser. From there, water flows into a series of domestichot water storage tanks. A large volume of water and domestic hot waterstorage is required due to short cycling of the heat pump compressors.There is a need for a heat pump water heater that negates the need fordomestic hot water storage and will provide instantaneous domestic hotwater on demand, while improving energy efficiency. Domestic hot waterstorage may be employed, but a large water storage facility is notrequired.

A typical domestic water heat pump heats the domestic water directlywithin the condenser of the heat pump. These systems are dead bandcontrolled and the temperature of the heated domestic water fluctuatessignificantly. The fluctuations in temperature are dampened by insertionof one or more storage tanks in the domestic hot water system downstreamof the heat pump.

SUMMARY OF THE INVENTION

The instantaneous hot water appliance uses three loops. The first loopis an open loop that receives source water. Heat is extracted from thesource water by a heat pump. The heat is supplied to a utility liquid,such as water, that is circulated within a closed loop. The resultingcooled source water may be used for other purposes. Heat exchangebetween the utility water in the closed loop and a second open loopheats domestic hot water within the second open loop. Domestic hot wateris available on demand, eliminating or reducing the need for domestichot water storage tanks and storage of large quantities of domestic hotwater. In the present invention, fluctuations in condenser watertemperature are dampened internally by a compressor control system asdescribed herein that may be supplemented by a condenser water buffer.

BRIEF DRAWING DESCRIPTION

FIG. 1 is a schematic of an embodiment of an instantaneous domestic hotwater heat pump according to the invention.

FIG. 2 shows a schematic of an embodiment of a heat pump that may beused with the invention.

DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 1 demonstrates an instantaneous domestic hot water heat pump thatis useful for multi-family residential and/or commercial applications.FIG. 1 shows: buffer 100, expansion tank 110, double-walled heatexchanger 120, circulating pump 130, water-to-water heat pump 140,temperature control valve 170, temperature sensor 160, and temperaturecontroller 150.

As shown in the drawing figures, an embodiment of the device utilizesthree loops in which water is circulated. The first open loop is sourcewater supplied to the evaporator 340 of the water-to-water heat pump140, FIG. 2 . The water may be supplied from the building water coolingsystem (such as a cooling tower) or other source at the source inlet.Source water external to the water-to-water heat pump circulation systementers from the building cooling system, or other source, at the sourceinlet as shown to provide water to the water-to-water heat pump 140. Insome embodiments, external water may be provided to the water-to-waterheat pump circulation system from another source.

A utility liquid is circulated by pump 130 in a closed loop, orcondenser water system, which is a closed loop. In the embodiment shownin FIG. 1 , the utility liquid is heated by a heat pump 140. The utilityliquid travels through water-to-water heat pump 140, to condenser waterbuffer 100 and then to double-walled heat exchanger 120. The utilityliquid returns to the water-to-water heat pump 140 after exiting thedouble-walled heat exchanger 120.

The utility liquid may be non-potable water (utility water). Since thewater is non-potable, additives may be introduced to the utility wateror liquid, such as glycols to retard freezing. Silicone fluids could beused. Double walls in the closed loop are preferred to further reducethe likelihood of contamination of the water in the second open waterloop. While the liquid in the closed loop could be liquids other thanwater or mixtures of water and other materials, water is used herein asan example of the liquid in the closed loop for explaining the operationof the invention.

In the second open water loop, domestic potable water external to theheat pump circulation system enters from the building domestic watersupply at a domestic potable water inlet and absorbs heat from thedouble-walled heat exchanger 120 in the embodiment shown. Domestic hotwater, heated in the double-walled heat exchanger 120, isinstantaneously available for use.

Water-to-water heat pump 140 may be an electric powered refrigerant heatpump in the embodiment as shown. The refrigerant used in the heat pumpcan be R134a, R410a, R514, R1233zd, carbon dioxide, or other(preferably, non-ozone depleting, low global warming potential)refrigerant. As shown in FIG. 2 , the refrigerant circulates through thewater-to-water heat pump 140 internally and in a closed loop. Therefrigerant is compressed in one or more compressors 310A/310B,condensed in an internal heat exchanger 320 (condenser) where heat isremoved, the refrigerant is expanded through an expansion valve 330, andevaporates in a separate internal heat exchanger 340 (evaporator) whereheat is absorbed into the refrigerant. A preferred heat pump operates ina Reverse Carnot Cycle, and provides two (2) heat exchangers, anevaporator and a condenser.

As shown in FIG. 2 , this invention embodies a condenser outlettemperature sensor 410, interconnected to controller 420. Controller 420utilizes algorithms for unique staging and control of the compressors310A/310B. Additional compressors may be provided in some embodiments.which may be variable frequency controlled, or controlled by a discretesignal. Dead band range control of compressors 310A/310B, controlled bycontroller 420 algorithms, provide operation and staging of thecompressors 310A/310B, preventing short cycling, thereby prolongingseamless operation of the compressors. Controller 420 monitors andcontrols the heat pump compressors (310A/310B) via a serial controlnetwork. Each compressor is staged On/Off, or speed controlled byvariable frequency drives, using individual temperature setpoints thatlimit the rate of temperature increase/decrease. Controller 420algorithms prevent compressor short cycling, which frequently occurswith conventional heat pump controllers. The outlet temperature sensor410 provides water temperature measurement and compares watertemperatures with temperature setpoints, for example, A, B, C, and D. Inthis example, the setpoint temperatures ascend as the alphabetical orderascends. Compressor 310A is actuated when sensor 410 senses the watertemperature decreasing to setpoint B, and is stopped when sensor 410senses the water temperature increasing to setpoint D. If needed to meetsystem demand, Compressor 310B is actuated when sensor 410 senses thewater temperature decreasing to setpoint A, and is stopped upon sensor410 senses the water temperature increasing to setpoint C. For variablespeed compressors, the compressor speed is modulated between thesetpoints. The lead and lag compressors may be periodically orcyclically alternated to equalize compressor runtimes.

The closed loop condenser system circulates utility water or utilityliquid through the condenser 320 of the water-to-water heat pump 140, inwhich heat has been absorbed into the utility water or utility liquid.The heated utility liquid or utility water then flows into the condenserwater buffer 100. The condenser water is circulated throughdouble-walled heat exchanger 120 using circulator 130. Domestic potablewater flows through the opposite side of the heat exchanger 120, withthe domestic hot water system of a building being an example of a waterloop, which is an open loop in most cases. Heat is exchanged from thecirculating condenser water or liquid in the closed loop thatinstantaneously heats the open domestic water loop as it leaves tosupport the building domestic hot water system.

Domestic hot water loads within a multi-family residential or commercialbuilding vary throughout the day. To meet varying demand, a temperaturecontrol loop may control the flow of condenser water through thedouble-walled heat exchanger 120 by changing the position of valve 170.Valve 170 is a three-way diverting valve with water entering one portand flowing out through two ports proportionate to the flow required tocontrol the temperature of the leaving domestic water as measured bysensor 160. An electronic temperature controller 150 changes theposition of the valve by an electronic signal to the valve actuator.

Source water from the building flows through the evaporator 340 and iscooled as it leaves the water-to-water heat pump 140 and returns to thebuilding in the embodiment as shown, which may be downstream of thesource outlet. Typically, source water originates from the buildingcooling water system. Expected water-to-water heat pump Coefficient ofPerformance (COP) is greater than 3.5 Consequently, this inventionallows for simultaneous production of cooled water and heated domesticwater, which may provide a typical Simultaneous Coefficient ofPerformance (SCOP) greater than 6.0. The simultaneous cooling ofbuilding water may be utilized to supplement building cooling. Producingboth hot water for use in baths, kitchens and the like while alsoproducing water for building cooling represents efficient energy usage,and reduces facility energy consumption.

Water exiting the heat pump in the closed loop is not uniform intemperature. In the present invention, fluctuations in utility watertemperature may be dampened internally in the condenser water buffer 100and controller 420. The buffer 100 mixes utility water to equalizedifferences in temperature. Further, the temperature of the domestic hotwater is controlled with a modulating control valve 170 and temperaturecontroller 150 on the flow of utility water to double-walled heatexchanger 120. Domestic hot water supply temperature sensor 160 measuresthe outlet water temperature and temperature controller 150, through aproportional/integral/derivative control loop, modulates control valve170 based on instantaneous requirements. The system preferably provideswater from the closed loop to heat exchanger 120 having a temperaturethat is plus or minus 0.5° F.

Buffer 100 acts as a hydraulic and thermal buffer that allows variationsin water temperature from heated utility water received from the heatpump 140 to equalize. Buffer 100 is positioned in the closed loop of theutility water system between the heat pump and the heat exchanger 120.In a preferred embodiment, the volume of utility water closed loop,including buffer 100, is no more than 25% of storage tank volume used ina domestic hot water system of conventional heat pump water heaters, inwhich a heat pump directly heats the domestic hot water, since thebuffer is for control of water temperature and not for water storage.The buffer could be defined by piping, such as oversized piping,positioned between the heat pump condenser and the heat exchanger 120.In the present invention, buffer 100 may not be used with systemsemploying heat pumps with variable speed compressors.

An expansion tank 110 communicates with the buffer 100 to accommodatethermal expansion of the utility water. A diaphragm or bladder in theexpansion tank keeps the pressure in the expansion tank substantiallyconstant.

While the utility water system is defined as a closed loop, provisionmay be made to add water to the utility water system due to evaporationor other water loss due to operation or otherwise. The operationalpressure of the system should be maintained, and water volume in thesystem is a factor in maintaining operational pressure.

In addition, when the domestic water system pressure is elevated due tothe height of the building, the double-walled heat exchanger 120 in thissystem isolates the lower operating pressure heat pump components fromthe elevated pressure in the domestic water system. The double walledheat exchanger aids in preventing system leaks which may contaminate thedomestic water. If the interior wall develops a leak, the water entersan area between the walls of the heat exchanger. A weep hole in thesecond wall allows limited flow from the weep hole, but signals that aleak is present in the heat exchanger, avoiding a catastrophic failure.In a conventional heat pump water heater, the hot water storage tankmust be designed for the elevated pressure as well as the condenserwater components of the heat pump.

In certain situations, the source water temperature is above the rangeof operation for the heat pump to function properly. Subassembly 200cooling loop may be provided to alleviate this problem. An additionalcirculating pump 210 may be added to the source water piping thatprovides water to the heat pump evaporator 340. This enables sourcewater to circulate the evaporator heat exchanger independently of theflow of external source water. Temperature controller 240 adjusts theposition of control valve 220 to allow source water to return to thecooling water system, thus causing additional flow of source water intothe evaporator. The temperature of the water at temperature sensor 230increases as additional source water from the source is introduced tothe evaporator 340, and decreases as less water is returned to thecooling or source water system.

This invention negates the need for domestic hot water storage andprovides instantaneous domestic hot water as needed. Domestic hot waterstorage may be utilized, but is not required. The device can beconstructed as a stand-alone appliance that can be inserted into thebuilding water system between the source water loop (the first openloop) and the domestic hot water system (the second open loop). In theevent that the appliance fails, it can be removed for repair orreplacement with another appliance inserted into the system between thesource water loop (first open loop) and the domestic hot water systemloop (the second open loop).

What is claimed:
 1. A water heating appliance, comprising: a first openwater loop that receives source water and discharges cooled sourcewater; a closed loop that circulates a liquid within the closed loop; asecond open water loop that receives potable domestic water anddischarges heated potable domestic water; a heat pump that extracts heatfrom the source water and provides the heat to the liquid in the closedloop producing heated liquid in the closed loop and producing the cooledsource water for discharge from the first open water loop; a firstcompressor that regulates a temperature of the heated liquid in theclosed loop; a heat exchanger that transfers heat from the heated liquidin the closed loop to the domestic potable water in the second openwater loop producing the heated potable domestic water.
 2. A waterheating appliance as described in claim 1, further comprising a secondcompressor that regulates the temperature of the heated liquid in theclosed loop.
 3. A water heating appliance as described in claim 1,further comprising a sensor that measures temperature of heated wateravailable for discharge from the second open water loop and a controllerthat actuates the first compressor in response to the sensor.
 4. A waterheating appliance as described in claim 2, further comprising a sensorthat communicates with utility water exiting a condenser, and acontroller, wherein the controller actuates the first compressor whenthe utility water exiting the condenser decreases to a first temperatureand terminates actuation of the first compressor of the heat pump whenthe utility water exiting the condenser reaches a second temperaturethat is higher than the first temperature, and the controller actuates asecond compressor of the heat pump when the utility water exiting thecondenser decreases to a third temperature and terminates actuation ofthe second compressor of the heat pump when the utility water exitingthe condenser reaches a fourth temperature.
 5. A water heating applianceas described in claim 1, the closed loop further comprising atemperature control loop that communicates with the heat exchanger, thetemperature control loop comprising a three-way diverting valve whereinwater enters a first port of the three way and the water flows from twoports of the three-way diverting valve proportionate to a flow requiredto control the temperature of the heated potable domestic water.
 6. Awater heating appliance as described in claim 1, the first open waterloop comprising a cooling loop that enables source water to circulate toa heat pump evaporator independently of external source water, the openwater loop comprising a temperature controller that controls a positionof a control valve causing source water to return to the first openwater loop.
 7. A water heating appliance as described in claim 1,further comprising a hydraulic and thermal buffer positioned within theclosed loop between the first compressor and the heat exchanger, thehydraulic and thermal buffer constructed and arranged to equalize asupply of the liquid to the heat pump.
 8. A water heating appliance asdescribed in claim 1, wherein source water is received into the firstopen water loop from a building cooling system.
 9. A water heatingappliance as described in claim 1, wherein source water is received intothe first open water loop from the building cooling system and thecooled source water is discharged from the first open water loop into abuilding cooling system.
 10. A water heating appliance as described inclaim 1, wherein source water is received into the first open water loopfrom the building cooling system and the cooled source water isdischarged from the first open water loop into a building cooling systemof a multi-family residential building.
 11. A water heating appliance asdescribed in claim 1, wherein the liquid in the closed loop compriseswater.
 12. A water heating appliance as described in claim 1, whereinthe liquid in the closed loop comprises water and glycol.
 13. A waterheating appliance as described in claim 1, wherein the heated potabledomestic water is supplied to a multi-family residential building.
 14. Awater heating appliance as described in claim 1, wherein the heatexchanger in the closed loop is a double-walled heat exchanger.